It is known that it is possible to obtain a powerful laser pulse at a wavelength of 1.3 microns by means of a device having an iodine gas laser oscillator which emits a short pulse into an iodine amplifier disposed at the output of the oscillator.
The oscillator can either be of the Q-switched type with a pulse cutter or of the "locked mode" type emitting a series of successive pulses; the "locked mode" type of oscillator having a device suitable for selecting one pulse from the series. In both cases, the output signal obtained at the output of the oscillator has a duration in the order of one nanosecond or of a fraction of a nanosecond.
The above-described laser generator devices have the disadvantage of delivering output pulses whose power is limited.
This disadvantage is explained by the fact that it is difficult to obtain very short pulses in an iodine laser without considerably increasing the pressure of the active gas.
Also, the upper level of the iodine is excited by photodissociation.
This upper level has two sub-levels and the lower denergizing level of the excited electrons has four sub-levels. Therefore, in theory, the laser emission caused by the excitation of an iodine gas should have eight distinct lines each corresponding to the various transition combinations between the two upper sub-levels and the four lower sub-levels.. In actual fact, only six lines are permitted. In the known lasers described above, it is observed that in practice, the iodine oscillator emits on only one preferential wavelength which corresponds to the emission line which provides the greatest gain. In these conditions, the energy amplification in the amplifier takes place only at this preferential wavelength, this reducing the output power of the device.
It is possible to mitigate this disadvantage to some extent by increasing the active gas pressure in the amplifier. Indeed, the relaxation periods between the preferential de-energizing sub-level and the lower sub-levels are then reduced and their values tend to be brought closer to that of the duration of the pulse. The energy amplification then increases. But the power increase of the output pulses thus obtained is small.
An attempt was therefore made to operate the iodine oscillator on the various emission lines of iodine, e.g. by disposing in the cavity a Perot-Fabry etalon (i.e. standard interference cavity) so as to modulate the gain on the various transitions. However, all the solutions brought forward have the disadvantage of being very difficult to implement. Preferred embodiments of the present invention mitigate the disadvantages of the above-described devices and produce a laser generator device suitable for emitting pulses having a wavelength of 1.3 microns with higher power than those produced according to the prior art.